GHRIL Infra Red De Rotator TCS Alignment Example Session
# GHRIL Infra Red De Rotator TCS Alignment Example Session

# Abstract

This page contains an alignment session from 22 Jul 1999. Seven
plots were taken and four changes were made to the TCS variables
controlling the de-rotator corrections.

# First attempt

A star was chosen with a 2" offset from the optical centre
and the auto guider set to guide, with loggin on.
We used the HANDSET to move the rotator in 45 degree increments. This
appeared suspect at the time, but we worked through and this is the
plot it produced : First FIT2D Plot
. This is missing about a 90 degree chunk of data. We phoned
Frank in Edinburgh and he told us to use the "ROT SKY" command.
We used this command with all subsequent tests with mostly 50 degree increments.
# Second FIT2D Plot

This one was better and produced a graph with two visible
circles, Plot and
Plot with FIT curve.
This produced the following numerical data
and was used to update the TCS common block using
DCL script for GSEXAM.
# The Third

This one was too closley centered and we decided not to use it
note the resolution of the circle : it is just over one arc second.
Plot and
Plot with FIT curve.
This produced the following numerical data
This was ** NOT ** used to update the TCS common block.
# Number Four

This one was better and produced a graph with two almost merged
circles, Plot and
Plot with FIT curve.
This produced the following numerical data
and was used to update the TCS common block using
DCL script for GSEXAM.
# The Fifth

This one was perhaps slightly better
Plot and
Plot with FIT curve.
This produced the following numerical data
and was used to update the TCS common block using
DCL script for GSEXAM.
# The Sixth

This one appeared no better really, but the data it provided was used
to update the TCS.
Plot and
Plot with FIT curve.
This produced the following numerical data
and was used to update the TCS common block using
DCL script for GSEXAM.
# The Seventh

This one was no better and produced a graph with two visible
circles, Plot and
Plot with FIT curve.
This produced the following numerical data
These data were not used and we stopped performing the tests.
# To Conclude

The De-rotator is now aligned by/corrected by TCS to a much greater degree, and the figures
from the Sixth run will be used to update the TCS.
The Values to Use for updating the
TCS would be directly entered into the fortran OWNINIT.FOR file
and a new version of TCS will be compiled. However Frank saw these and said that he would prefer more accurate results. Bearing in mind that it was three in the morning I had decided to give the telescope time to the astronomer. With hindsight I should have performed perhaps two more tests. However the results from this would give a maximum movement of .3 arc seconds over an entire 720 degree rotation and are much better than we started with.

R.P. Clark.
E-mail: rclark@ing.iac.es
* Last Updated 14th January 2000. *